Continuous Reaction Process For Preparing Metallic Nanoparticles

ABSTRACT

A method for producing metallic nanoparticles in a continuous flow-through reactor comprising combining at least one metallic precursor and at least one radical precursor in a reactant reservoir to form a reactant stream; flowing the reactant stream through at least one channel having a first channel end connected to the reactant reservoir, a second channel end connected to a product reservoir, and at least one clear channel section, which is transparent to activating radiation used to generate a radical reducing agent from the radical precursor, for exposing the reactant stream to a radiation source; exposing the reactant stream in the clear channel section to the radiation source to generate the radical reducing agent, initiate a reaction, and form a product stream comprising metallic nanoparticles; and optionally, collecting the product stream in the product reservoir.

CROSS-REFERENCE TO RELATED APPLICATIONS

Commonly assigned U.S. patent application Ser. No. 12/126,581, ofMichelle Chrétien et al., filed May 23, 2008, entitled “PhotochemicalSynthesis of Metallic Nanoparticles For Ink Applications,” which ishereby incorporated by reference herein in its entirety, discloses amethod of forming an ink comprising photochemically producing stabilizedmetallic nanoparticles and formulating the nanoparticles into an ink.

Commonly assigned U.S. patent application Ser. No. 12/133,548, ofMichelle Chrëtien et al., filed Jun. 5, 2008, entitled “PhotochemicalSynthesis of BiMetallic Core-Shell Nanoparticles,” which is herebyincorporated by reference herein in its entirety, discloses a method ofphotochemically producing bimetallic core-shell nanoparticles, which canbe used in ink applications.

TECHNICAL FIELD OF THE DISCLOSURE

The present disclosure relates to a continuous reaction process forpreparing metallic nanoparticles.

BACKGROUND

Printed electronic features, such as thin film transistor (TFT)electrodes and radio frequency identification (RFID) technology, are anarea of intensive research. The ability to directly print electronicfeatures opens the door to a myriad of low-cost flexible electronicswith many possibilities for application.

Materials commonly used for printing electronic features include metalmaterials. In particular, nanoparticulate metal materials arewidely-used in printed electronics applications because they havesuperior characteristics that yield a better product. Metallicnanoparticles are particles having a diameter in the submicron sizerange. Nanoparticle metals have unique properties, which differ fromthose of bulk and atomic species. Metallic nanoparticles arecharacterized by enhanced reactivity of the surface atoms, high electricconductivity, and unique optical properties. For example, nanoparticleshave a lower melting point than bulk metal, and a lower sinteringtemperature than that of bulk metal. The unique properties of metalnanoparticles result from their distinct electronic structure and fromtheir extremely large surface area and high percentage of surface atoms.Metal nanoparticles, then, can potentially enable production of lowcost, flexible electronics. For example, once synthesized and isolated,metal nanoparticles can be dispersed into an ink vehicle, and the inkcan be printed on a desired substrate to form an electronic pattern. Themetal particles can then be annealed to form a conductive film. Thespecific metal selected for the nanoparticle can be varied in accordancewith the specific application.

Methods have been proposed for preparing metal particles. For example,metal nanoparticles can be synthesized using a photochemical process.U.S. patent application Ser. No. 12/126,581, which is herebyincorporated by reference herein in its entirety, discloses a method offorming an ink comprising photochemically producing stabilized metallicnanoparticles and formulating the nanoparticles into an ink.

U.S. patent application Ser. No. 12/133,548, which is herebyincorporated by reference herein in its entirety, discloses a method ofphotochemically producing bimetallic core-shell nanoparticles, which canbe used, for example, in ink applications.

U. S. Patent Publication 20090142481, which is hereby incorporated byreference herein in its entirety, discloses a low-cost coppernanoparticle ink that can be annealed onto a paper substrate for RFIDantenna applications using substituted dithiocarbonates as stabilizersduring copper nanoparticle ink production.

U.S. Pat. No. 7,494,608, which is hereby incorporated by referenceherein in its entirety, discloses a composition comprising a liquid anda plurality of silver-containing nanoparticles with a stabilizer,wherein the silver-containing nanoparticles are a product of a reactionof a silver compound with a reducing agent comprising a hydrazinecompound in the presence of a thermally removable stabilizer in areaction mixture comprising the silver compound, the reducing agent, thestabilizer, and an organic solvent wherein the hydrazine compound is ahydrocarbyl hydrazine, a hydrocarbyl hydrazine salt, a hydrazide, acarbazate, a sulfonohydrazide, or a mixture there and wherein thestabilizer includes an organoamine. See also U.S. Pat. 7,270,694, whichis hereby incorporated by reference herein in its entirety.

U. S. Patent Publication 20090148600, which is hereby incorporated byreference herein in its entirety, discloses metal nanoparticles with astabilizer complex of a carboxylic acid-amine on a surface thereofformed by reducing a metal carboxylate in the presence of an organoamineand a reducing agent compound. The metal carboxylate may include acarboxyl group having at least four carbon atoms, and the amine mayinclude an organo group having from 1 to about 20 carbon atoms.

The appropriate components and process aspects of the each of theforegoing U. S. Patents and Patent Publications may be selected for thepresent disclosure in embodiments thereof. Further, throughout thisapplication, various publications, patents, and published patentapplications are referred to by an identifying citation. The disclosuresof the publications, patents, and published patent applicationsreferenced in this application are hereby incorporated by reference intothe present disclosure to more fully describe the state of the art towhich this invention pertains.

Currently available methods for preparing metallic nanoparticles aresuitable for their intended purposes. However, a need remains for animproved, reliable, cost-effective system and method suitable forpreparing metallic nanoparticles, bimetallic nanoparticles, and thelike. Further, a need remains for an improved system and method forpreparing metallic nanoparticles that are suitable for printingelectronic features such as by incorporation into inks. Further, a needremains for an improved system and method for preparing metallicnanoparticles that are stable under atmospheric conditions, have a smallparticle size, and where the particles formed are of a size such thatthey can be annealed at lower temperatures (<200° C.) so that they canbe used with substrates such as paper and plastics. Further, a needremains for a system and method for preparing metallic nanoparticleswhich provides cost-effectiveness and a high throughput yield. Further,a need remains for an improved system and method for preparing metallicnanoparticles in production sized quantities.

SUMMARY

Described is a method for producing metallic nanoparticles in acontinuous flow-through reactor comprising combining at least onemetallic precursor and at least one radical precursor in a reactantreservoir to form a reactant stream; flowing the reactant stream throughat least one channel having a first channel end connected to thereactant reservoir, a second channel end connected to a productreservoir, and at least one clear channel section, which is transparentto activating radiation used to generate a radical reducing agent fromthe radical precursor, for exposing the reactant stream to a radiationsource; exposing the reactant stream in the clear channel section to theradiation source to generate the radical reducing agent, initiate areaction, and form a product stream comprising metallic nanoparticles;and optionally, collecting the product stream in the product reservoir.In embodiments, two or more different metallic precursors can becombined to provide metal alloy nanoparticles.

Further described is a method for producing bimetallic or alloynanoparticles in a continuous flow-through reactor comprising combiningat least one first metallic precursor and at least one first radicalprecursor; combining at least one second metallic precursor and at leastone radical precursor; wherein the first and second metallic precursorsare the same or different; and wherein the first and second radicalprecursors are the same or different; flowing the first metallicprecursor, and first radical precursor, second metallic precursor, andsecond radical precursor through a first clear channel section of thereactor and exposing the metallic and radical precursors to a radiationsource to initiate a reaction and form a product stream comprisingmetallic or bi-metallic nanoparticles having a core-shell configuration,an alloy configuration, or a combination thereof; and optionally,collecting the product stream in a product reservoir.

Further described is a continuous flow-through reactor system forproducing metallic nanoparticles comprising at least one reactantreservoir for combining at least one metallic precursor and at least oneradical precursor in to form a reactant stream; at least one productreservoir; at least one channel having a first end fluidly connected tothe reactant reservoir and a second end fluidly connected to the productreservoir for flowing the reactant stream there through, wherein atleast one channel has at least one clear channel section which istransparent to activating radiation used to generate a radical reducingagent from the radical precursor; at least one device for causing thereactant stream to flow from the reactant reservoir through the clearchannel section to the product reservoir; at least one radiation sourcecapable of exposing the reactant stream passing through the clearsection channel.

Further described is a continuous flow-through reactor system comprisingat least one first reactant reservoir for combining at least one firstmetallic precursor and at least one first radical precursor in to form afirst reactant stream; at least one second reactant reservoir forcombining at least one second metallic precursor and at least one secondradical precursor in to form a second reactant stream; wherein the firstand second metallic precursors are the same or different; and whereinthe first and second radical precursors are the same or different; atleast one first channel having at least one first clear channel section,a first end fluidly connected to the first reactant reservoir, and asecond end fluidly connected to the product reservoir, for flowing thefirst reactant stream through the first clear channel section to exposethe first reactant stream to a radiation source to initiate a reactionand form a first product stream comprising metallic nanoparticles; atleast one second channel having at least one second clear section, afirst end fluidly connected to the second reactant reservoir, and asecond end fluidly connected to the first channel downstream of thefirst clear channel section, for flowing the second reactant stream andthe first product stream through the second clear channel section toproduct a second product stream comprising bimetallic nanoparticleshaving a core-shell configuration, an alloy configuration, or acombination thereof.

The advantages of the present disclosure are numerous. The metallic,bimetallic, and alloy nanoparticles herein may be annealed at a lowertemperature than the large particle conventional annealing temperature.For example, the nanoparticles herein can be annealed at a temperatureof from about 80 to about 300, or from about 100 to about 200° C. ratherthan large particle annealing temperatures of from about 800 to about1,500° C. Therefore, inks or other materials containing the presentnanoparticles can be printed on a wide variety of substrates, includingpaper and plastic substrates. The method is also fast, and thus largequantities of nanoparticles can be produced rapidly, in a matter ofseconds to a few minutes. The method is also versatile. Bare,unprotected nanoparticles are produced, and the nanoparticles can bestabilized with virtually any molecule by extracting the nanoparticlesinto an organic solvent containing a stabilizer of choice. Additionally,there are numerous combinations of metals and reducing radical pairsthat may be used in this method. For instance, copper can be used inthis method. Therefore, this method offers a cheaper alternative tosynthesis of metallic nanoparticles using more expensive metals, such asplatinum, gold or silver. The size and/or concentration of thenanoparticles can be easily controlled by changing one or more of theparameters of this method, such as irradiation time, irradiationintensity, the metal counter-ion used, and/or the concentrations of themetal or the photoinitiator. Further, the method isecologically-friendly because it does not require harsh reducing agents,and can be performed at room temperature in water.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an illustration of a continuous reaction process and systemfor preparing metallic nanoparticles in accordance with the presentdisclosure.

FIG. 2 is an illustration of a continuous reaction process and systemfor preparing bimetallic nanoparticles in accordance with the presentdisclosure.

FIG. 3 is an illustration of an alternate continuous reaction processand system for preparing metallic nanoparticles in accordance with thepresent disclosure.

FIG. 4 is an illustration of another continuous reaction process andsystem for preparing metallic nanoparticles in accordance with thepresent disclosure.

DETAILED DESCRIPTION

Disclosed is a method comprising using a continuous flow-through reactorfor a mono, bimetallic or metal alloy nanoparticle synthesis reaction.The reactants flow through a tubular reactor of which a clear section ofthe tube is exposed with radiation such as ultra-violet or visible lightto initiate the photochemical reaction. The small cross-section of thereactor tube ensures that a maximum amount of the reactants are exposedto the UV light, thus maximizing the reaction efficiency. The reactorand method can be readily scaled up. In embodiments, a large reservoirof reactants can be directed into multiple tubes, branched tubes, andthe like. In embodiments, uni-metallic, bi-metallic or alloynanoparticles can be prepared in a single tubular reactor or in a seriesof branched tubular reactors. In one embodiment, at least one channelcomprises a single channel having a plurality of branches extendingtherefrom, and wherein each branch has at least one clear channelsection. In another embodiment, at least one channel comprises aplurality of channels, each channel having at least a first channel endconnected to the reactant reservoir, a second channel end connected tothe product reservoir, and at least one clear channel section forexposing the reactant stream to a radiation source.

In embodiments, the metallic nanoparticles are gold, silver, copper,platinum, palladium, nickel, lead, rhodium, or combinations thereof. Ina specific embodiment, the metallic nanoparticles comprise copper aloneor as part of a bimetallic nanoparticle system.

Generally, metallic nanoparticles may be produced in an aqueous solutionby reduction of one or more metallic ions with at least one reducingagent provided as an aqueous solution of reducing agent precursor andmetallic salt. The aqueous solution may be de-aerated. The metalnanoparticle synthesis reaction may be conducted in aqueous solution byreduction of a metal salt by a photochemically generated reducingspecies (such as α-hydroxy or α-amino radicals) as follows

wherein R′—R is a reducing agent precursor;

.R′ and .R are photochemically generated radicals,

M^(n+) is a metal cation and n is a number; and

M⁰ is a metal atom and ultimately a metal nanoparticle.

Alternately, the solutions can be non-aqueous, that is, prepared with anorganic solvent, provided that the reducing agent and the salt dissolvein the chosen solvent.

The metallic precursor can comprise one or more metallic salts. Suitablemetallic ions provided as metal salts include ions of copper, aluminum,magnesium, manganese, zinc, chromium, lead, cadmium, cobalt, nickel,gold, silver, platinum, tin, palladium, indium, iron, tungsten,molybdenum, ruthenium, bismuth, other suitable metal ions, and mixturesthereof. In specific embodiments, suitable metallic ions include copper,aluminum, magnesium, zinc, chromium, lead, cadmium, cobalt, nickel,gold, silver, platinum, tin, palladium, iron, tungsten, other suitablemetal ions, and mixtures thereof. For example, the metal salt can beprovided in the form of metal sulfates, metal halides (such as metalchlorides or metal bromides), metal nitrates, metal acetates, metalnitrites, metal oxides, metal carbonates, metal oxalates, metalpyrazolyl borates, metal azides, metal fluoroborates, metalcarboxylates, metal halogencarboxylates, metal hydroxycarboxylates,metal aminocarboxylates, metal aromatic and nitro and/or fluorosubstituted aromatic carboxylates, metal aromatic and nitro and/orfluoro substituted aromatic carboxylates, metal sulfonates, and thelike.

In one embodiment, the metal ions are provided as copper (II) ions. Thecopper (II) ions can be incorporated into metal salts such as, forexample, copper sulfate, copper chloride, copper nitrate, or copperacetate. Of course, other metals, and other metal salts, can also beused.

As the reducing agent, one or more photochemically generated radicalsmay be used. Radical precursors (reducing agent precursors) areactivated upon exposure to radiation to produce the radical. Theradicals react with one or more metal cations (M⁺, M²⁺, etc., wherein Mrepresents a suitable metal), to produce M⁰ metal atoms and ultimatelyunprotected metal nanoparticles. Suitable radical reducing agentsinclude, for example, ketyl, α-amino, phosphinoyl, benzoyl, and acylradicals. The radicals used according to the present disclosure may beprovided from any known source, including commercially availablesources. In one embodiment, the radicals are produced by Norrish Type Icleavage of α-hydroxy or α-aminoketones. Such radical precursors arecommercially available as, for example, Ciba commercial photoinitiatorsIrgacure® 184, 127, 2959, 369, 379, etc. In another embodiment, theradicals are produced by a Norrish Type II photoinitiation process, inwhich a photoexcited ketone (such as, for example, benzophenone)abstracts a proton from a proton donor molecule (such as, for example,isopropanol) to generate two ketyl radicals.

In embodiments, the aqueous solution of metallic nanoparticles and theradical reducing agent are irradiated for from about 5 seconds to about90 seconds, such as from about 10 to about 45 seconds or from about 15to about 30 seconds, although not limited. The intensity of irradiationis from about 0.001 W/cm² to about 10 W/cm², such as from about 0.05W/cm² to about 5 W/cm², or from about 0.1 W/cm² to about 1 W/cm²,although not limited. The source of irradiation may generally be anysource known in the art, such as, for example, by ultra-violet (UV) orvisible radiation or any radiation wherein the radical precursor absorbsthe wavelengths of radiation being used. In embodiments, this results inthe synthesis of uncoated metallic nanoparticles.

The metallic nanoparticles produced are desirably in the nanometer sizerange. For example, in embodiments, the metallic nanoparticles have anaverage particle size (such as particle diameter or longest dimension)of from about 1 to about 1000 nanometers (nm), such as from about 50 toabout 500 nm, or about 100 to about 200 nm, or about 5 to about 400 nm,or about 30 to about 400 nm, or about 2 to about 20 nm. Herein,“average” particle size is typically represented as d₅₀, or defined asthe volume median particle size value at the 50th percentile of theparticle size distribution, wherein 50% of the particles in thedistribution are greater than the d₅₀ particle size value, and the other50% of the particles in the distribution are less than the d₅₀ value.Average particle size can be measured by methods that use lightscattering technology to infer particle size, such as Dynamic LightScattering. The particle diameter refers to the length of the pigmentparticle as derived from images of the particles generated byTransmission Electron Microscopy.

The size of the nanoparticle formed may be controlled by changing theirradiation time and intensity, the metal counter-ion, modifying theconcentration of the metal ion and/or the photoinitiator, or by othermeans.

The metallic nanoparticles may be in any shape. Exemplary shapes of themetallic nanoparticles can include, without limitation, needle-shape,granular, globular, spherical, amorphorous shapes, and the like.

Once prepared, the uncoated metallic nanoparticles may be suspended inan aqueous solution. Unprotected, uncoated metallic nanoparticles may befunctionalized by any suitable means known in the art. Moreover, themetallic nanoparticles may be stabilized. Stabilization of the particlesmay be achieved by adding stabilizing molecules directly to the aqueoussolution containing the nanoparticles. Alternatively, the nanoparticlescan be extracted into an organic solvent containing the stabilizingmolecules. For example, copper nanoparticles may be stabilized with asubstituted dithiocarbonate. In another example, silver nanoparticlesmay be stabilized with organic acids or amines, such as oleic acid oroleylamine. In another example, gold particles capped with alkylthiolcan be used. Other suitable stabilizers generally include, withoutlimitation, organic stabilizers. The term “organic” in “organicstabilizer” refers to, for example, the presence of carbon atom(s), butthe organic stabilizer may include one or more non-metal heteroatomssuch as nitrogen, oxygen, sulfur, silicon, halogen, and the like.Examples of other organic stabilizers may include, for example, thioland its derivatives, —OC(═S)SH (xanthic acid), dithiocarbonates,polyethylene glycols, polyvinylpyridine, polyninylpyrolidone, alkylxanthate, ether alcohol based xanthate, amines, and other organicsurfactants. The organic stabilizer may be selected from the groupconsisting of a thiol such as, for example, butanethiol, pentanethiol,hexanethiol, heptanethiol, octanethiol, decanethiol, and dodecanethiol;a dithiol such as, for example, 1,2-ethanedithiol, 1,3-propanedithiol,and 1,4-butanedithiol; or a mixture of a thiol and a dithiol. Theorganic stabilizer may be selected from the group consisting of axanthic acid such as, for example, O-methylxanthate, O-ethylxanthate,O-propylxanthic acid, O-butylxanthic acid, O-pentylxanthic acid,O-hexylxanthic acid, O-heptylxanthic acid, O-octylxanthic acid,O-nonylxanthic acid, O-decylxanthic acid, O-undecylxanthic acid,O-dodecylxanthic acid and combinations thereof.

Bi-metallic nanoparticles can be formed by forming core particles andforming a shell over the core particles to provide the bi-metalliccore-shell nanoparticles.

The material that forms the shell can be any suitable metal that willprovide the desired properties, such as conductivity and the like. Thematerials used to form the shell can be the same or different form thematerials used to form the core. Suitable shell materials includecopper, aluminum, magnesium, manganese, zinc, chromium, lead, cadmium,cobalt, nickel, gold, silver, platinum, tin, palladium, indium, iron,tungsten, molybdenum, ruthenium, bismuth, or other suitable elementalmetals and mixtures and alloys thereof. In specific embodiments,suitable shell materials include copper, aluminum, magnesium, zinc,chromium, lead, cadmium, cobalt, nickel, gold, silver, platinum, tin,palladium, iron, tungsten, other suitable shell materials, and mixturesthereof.

In some embodiments, the core and shell metals are different. Forexample, copper can be used as a core material in view of its low cost,while precious metals can be used as a shell material in view of theirstability to oxygen and high conductivity properties. Such combinationsallow for core-shell nanoparticles that can be produced at low cost butwith desirable properties.

In embodiments, the uncoated or functionalized metallic or bimetallicnanoparticles are dispersed in the appropriate vehicle for formulationinto an ink.

FIG. 1 illustrates an embodiment of the present method and system 100for producing metallic nanoparticles in a continuous flow-throughreactor. System 100 includes a reactant reservoir 102 for combining atleast one metallic precursor and at least one reducing agent to form areactant stream 104 comprising an aqueous solution of radical precursor(reducing agent) and metallic salt. A device such as a pump 106 isprovided for flowing the reactant stream 104 through the at least onechannel having at least one clear channel section 108 that istransparent to the activating radiation used. Alternately, the systemsand processes herein can be configured such that gravity enables thestream or streams to flow there through in the desired manner. Thereactant stream 104 is exposed to any suitable irradiation source suchas visible light source or a UV light source 114 for exposing thereactant stream to radiation 116 in the clear channel section toinitiate a reaction and form a product stream 110 comprising metallicnanoparticles in an aqueous suspension. Optionally, the produced productstream can be collected in the product reservoir 112 where the aqueoussuspension of metal nanoparticles can be stored or transferred toanother vessel.

The system and method illustrated in FIG. 1 is shown as a single channelwith a single clear channel section. The present disclosure is notlimited to this configuration, however. Numerous alternativeconfigurations are contemplated such as, for example, wherein the atleast one channel comprises a single channel having a first end fluidlyconnected to the reactant reservoir 102 and a plurality of branchesextending therefrom to form a plurality of reactant stream branches, andwherein each branch has at least one clear channel section. FIG. 2,described further below, illustrates an embodiment for preparingbi-metallic or alloy nanoparticles having a core-shell or alloyconfiguration. FIG. 3 illustrates one possible embodiment for a branchedsystem and process herein wherein system 300 includes a reactantreservoir 302 having a branched channel 304 extending therefromincluding branches 306, 308, 310, and 312 each branch fluidly connectedto the reactant reservoir 302. Devices such as pumps 314, 316, 318, 320are provided for flowing reactant streams 322, 324, 326, 328 throughtheir respective channels. Branch 306 has a clear channel section 330.Branch 308 has a clear channel section 332. Branch 310 has a clearchannel section 334. Branch 312 has a clear channel section 336.Reactant streams 322, 324, 326, 328 flow through their respectivebranches to clear channel sections 330, 332, 334, 336 where they areexposed to irradiation 338, 340, 342, 344 from UV light sources 346,348, 350. UV light source 348 may be configured with multiple lights soas to irradiate clear channels 332, 334 as illustrated in FIG. 3.Alternately, separate UV light sources can be provided. Reactions areinitiated in the clear channel sections 330, 332, 334, 336 and productstreams 352, 354, 356, 358, are formed and collected in productreservoir 360. Again, numerous variations are contemplated, such asmultiple reactant reservoirs containing the same or different reactants,additional branched channels containing one or more clear channelsections, a plurality of radiation sources wherein the reactant streamin each clear channel section is exposes to at least one of theplurality of radiation sources, one or more irradiation sources andtypes, and one or more collection reservoirs.

In another embodiment, the at least one channel can include a pluralityof individual channels, each channel having at least a first channel endconnected to a larger reactant reservoir, or connected to a plurality ofindividual reactant reservoirs, a second channel end connected to theproduct reservoir, and at least one clear channel section in each forexposing the reactant stream to a radiation source. FIG. 4 illustratesone possible embodiment wherein system 400 includes a reactant reservoir402 having a first channel 404, a second channel 406, and a thirdchannel 408 extending from and fluidly connected to the reactantreservoir 402. Devices such as pumps 410, 412, and 414 are provided forflowing reactant streams 414, 416, 418 through their respectivechannels. First channel 404 has a clear channel section 420. Secondchannel 406 has a clear channel section 422. Third channel 408 has aclear channel section 424. Reactant streams 414, 415, and 418 flowthrough their respective channels to clear channel sections 420, 422,424 are exposed therein to irradiation 426, 428, 430 from UV lightsources 432, 434, 436. Reactions are initiated in the clear channelsections 420, 422, 424 and product streams 438, 440, and 442 are formedand collected in product reservoir 444. As described herein, numerousvariations are contemplated, such as multiple reactant reservoirscontaining the same or different reactants, additional channelscontaining one or more clear channel sections, one or more irradiationsources and types, and one or more collection reservoirs.

The process can further include providing a plurality of radiationsources; and exposing the reactant stream in each clear channel sectionto at least one of the plurality of radiation sources. The plurality ofradiation sources can include two or more radiation sources disposed toirradiate one or more of the clear channel sections, wherein theradiation sources are the same or different. Different types ofradiation sources can be provided, for example, so that differentchemical reactions can be initiated in different channels or branches ofthe same reaction system and process.

In embodiments, the channels comprise reactor tubes having smallcross-sectional areas such that a maximum amount of the reactants areexposed to the UV light, thus maximizing the reaction efficiency. Inembodiments, wherein the clear channel section has a cross-section offrom about 1 to about 500 millimeters, or from about 1 to about 10millimeters, or from about 1 to about 4 millimeters.

The continuous system herein can easily and inexpensively be upgraded tohigher throughput simply by adding more glass tubes into the system,compared to purchasing significantly more expensive bulk reactorequipment.

In another embodiment, a system and method for producing bimetallic oralloy nanoparticles or a combination thereof in a continuousflow-through reactor is described. In embodiments, the method comprisescombining at least one first metallic precursor and at least one firstradical precursor in a first reactant reservoir to form a first reactantstream; combining at least one second metallic precursor and at leastone second radical precursor in a second reactant reservoir to form asecond reactant stream; wherein the first and second metallic precursorsare the same or different; and wherein the first and second radicalprecursors are the same or different; flowing the first reactant streamthrough a first clear channel section of the reactor which istransparent to activating radiation used to generate a radical reducingagent form the radical precursor to expose the first reactant stream toa radiation source to initiate a reaction and form a first productstream comprising metallic nanoparticles; combining the producedmetallic nanoparticles with the second reactant stream downstream of thefirst clear channel section; flowing the produced metallic nanoparticlesand the second reactant stream through a second clear channel section ofthe reactor that is downstream of the first clear channel section;exposing the produced metallic nanoparticles and the second reactantstream to the radiation source to initiate a reaction and form a secondproduct stream comprising metallic or bi-metallic nanoparticles having acore-shell configuration, an alloy configuration, or a combinationthereof; and optionally, collecting the second product stream in asecond product reservoir.

Turning to FIG. 2, a continuous flow-through reactor system and method200 includes combining at least one first metallic precursor and atleast one first reducing agent in a first reactant reservoir 202 to forma first reactant stream 204. A device for flowing the streams such aspump 206 flows the first reactant stream to first clear channel section208 expose the first reactant stream to radiation source 214 whereirradiation 216 initiates a reaction to form a first product stream 210comprising metallic nanoparticles. At least one second metallicprecursor and at least one second reducing agent is combined in a secondreactant reservoir 203 to form a second reactant stream 205. A devicesuch as pump 207 can be used to flow second reactant stream 205 throughthe channels. Second reactant stream 205 is combined with the producedmetallic nanoparticles 210 downstream of the first clear channel section206. The produced metallic nanoparticles 210 and the second reactantstream 205 flow through a second clear channel section 211 of thereactor that is downstream of the first clear channel section 206 wherethe produced metallic nanoparticles 210 and the second reactant stream205 are exposed to the radiation source 214 where irradiation 216initiates a reaction to form a second product stream 212 comprisingbimetallic nanoparticles having a core shell or alloy configuration. Thesecond product stream 212 can be collected in product reservoir 218 ordisposed in an alternative vessel.

In embodiments, the first and second metallic precursors can be the sameor different, and the first and second reducing agents can be the sameor different.

Alternate embodiments contemplate formation of bimetallic or alloyparticles by premixing the two or more different metal salt and radicalprecursors in the same reservoir and irradiating the mixturesimultaneously. For example, the method can comprises premixing themetallic precursors and radical precursors in a single reservoir; andflowing the mixture combined in the single reservoir through at leastone clear channel section; exposing the mixture in the clear channelsection to the radiation source to initiate a reaction and form aproduct stream comprising metallic or bimetallic nanoparticles having acore-shell configuration, an alloy configuration, or a combinationthereof, and optionally, collecting the product stream in a producereservoir.

As with previous embodiments described herein, this embodiment is notlimited to a specific configuration, but rather numerous alternativeconfigurations are contemplated such as, for example, wherein thechannels comprise two are more branches, wherein each branch can beconnected to first, second, third, etc., reactant reservoirs, andwherein each branch has at least one clear channel section or whereineach reactant stream ultimately flows through a branch having a clearchannel section that can be treated to initiate a reaction.

Alternately, a plurality of individual channels can be provided, eachchannel having a first end connected to at least one reactant reservoir,a second end connected to a product reservoir, and at least one clearchannel section in each for exposing the reactant stream to a radiationsource.

Further, a plurality of radiation sources can be provided for exposingthe reactant streams in each clear channel section to at least one ofthe plurality of radiation sources. The plurality of radiation sourcescan include two or more radiation sources disposed to irradiate one ormore of the clear channel sections, wherein the radiation sources arethe same or different. Different types of radiation sources can beprovided, for example, so that different chemical reactions can beinitiated in different channels or branches of the same reaction systemand process.

EXAMPLES

The following Examples are being submitted to further define variousspecies of the present disclosure. These Examples are intended to beillustrative only and are not intended to limit the scope of the presentdisclosure. Also, parts and percentages are by weight unless otherwiseindicated.

Example 1

Monometallic copper nanoparticle. With reference to FIG. 1, an aqueoussolution containing 0.33 mM of a copper (I or II) salt and 1.0 mM ofIrgacure® 2959 (an α-hydroxyketone photoinitiator) is charged into areactant reservoir, degassed with argon for 5 minutes and then pumpedthrough a tubular reactor as described herein. The feed rate iscontrolled such that the solution is exposed to UV light in the clearportion of the reactor for a period of 15 to 90 seconds. The resultingslurry that feeds into the product reservoir consists of coppernanoparticles suspended in water. The particle size of nanoparticleranges from approximately 1 to 1000 nm depending on UV exposure time(longer exposure results in larger particle size).

Example 2 Bimetallic Copper-Silver Nanoparticle

Part A. With reference to FIG. 2, an aqueous solution containing 0.33 mMof a Cu (I or II) salt and 1.0 mM of Irgacure 2959® (an α-hydroxyketonephotoinitiator) is charged into a first reactant reservoir, degassedwith argon for 5 minutes, and then pumped through a first section of atubular reactor as described herein. The feed rate is controlled suchthat the solution is exposed to UV light for approximately 10 seconds inthe first clear section of the reactor. This results in a slurry of Cunanoparticles suspended in water.

Part B. An aqueous solution containing 0.33 mM HAuCl₄ and 1 mM Irgacure2959® is charged into a second reactant reservoir, degassed with argonfor 5 minutes, and then pumped into the tubular reactor such that itmixes with the solution prepared in Part A near the outlet of the firstclear section of the reactor. This mixed solution is exposed to UV lightfor 15 to 90 seconds in the second clear section of the reactor. Thisresults in a solution of Cu/Ag nanoparticles. The solution of Cu/Agnanoparticles can, for example, be collected and re-suspended in asolvent suitable for ink-jet printing.

It will be appreciated that various of the above-disclosed and otherfeatures and functions, or alternatives thereof, may be desirablycombined into many other different systems or applications. Also thatvarious presently unforeseen or unanticipated alternatives,modifications, variations or improvements therein may be subsequentlymade by those skilled in the art which are also intended to beencompassed by the following claims. Unless specifically recited in aclaim, steps or components of claims should not be implied or importedfrom the specification or any other claims as to any particular order,number, position, size, shape, angle, color, or material.

1. A method for producing metallic nanoparticles in a continuousflow-through reactor comprising: combining at least one metallicprecursor and at least one radical precursor in a reactant reservoir toform a reactant stream; flowing the reactant stream through at least onechannel having a first channel end connected to the reactant reservoir,a second channel end connected to a product reservoir, and at least oneclear channel section, which is transparent to activating radiation usedto generate a radical reducing agent from the radical precursor, forexposing the reactant stream to a radiation source; exposing thereactant stream in the clear channel section to the radiation source togenerate the radical reducing agent, initiate a reaction, and form aproduct stream comprising metallic nanoparticles; and optionally,collecting the product stream in the product reservoir.
 2. The method ofclaim 1, wherein the at least one channel comprises a single channelhaving a plurality of branches extending therefrom, and wherein eachbranch has at least one clear channel section; or wherein the at leastone channel comprises a plurality of channels, each channel having atleast a first channel end connected to the reactant reservoir, a secondchannel end connected to the product reservoir, and at least one clearchannel section for exposing the reactant stream to a radiation source.3. The method of claim 1, further comprising: providing a plurality ofradiation sources; and exposing the reactant stream in each clearchannel section to at least one of the plurality of radiation sources.4. The method of claim 1, wherein the radiation source is anultra-violet radiation source, a visible radiation source, or acombination thereof.
 5. The method of claim 1, wherein the clear channelsection has a cross-section of from about 1 to about 4 millimeters. 6.The method of claim 1, wherein the metallic precursor comprises one ormore metallic salts.
 7. The method of claim 1, wherein the metallicnanoparticles are gold, silver, copper, platinum, palladium, nickel,lead, or combinations thereof.
 8. The method of claim 1, wherein theradical reducing agent is a ketyl radical or an α-amino radical.
 9. Themethod of claim 1, wherein the metallic nanoparticles are from about 5nanometers to about 400 nanometers in size.
 10. A method for producingbimetallic or alloy nanoparticles in a continuous flow-through reactorcomprising: combining at least one first metallic precursor and at leastone radical precursor; combining at least one second metallic precursorand at least one radical precursor; wherein the first and secondmetallic precursors are the same or different; and wherein the first andsecond radical precursors are the same or different; flowing the firstmetallic precursor, and first radical precursor, second metallicprecursor, and second radical precursor through a first clear channelsection of the reactor and exposing the metallic and radical precursorsto a radiation source to initiate a reaction and form a product streamcomprising metallic or bimetallic nanoparticles having a core-shellconfiguration, an alloy configuration, or a combination thereof; andoptionally, collecting the product stream in a product reservoir. 11.The method of claim 10, wherein combining comprises combining at leastone first metallic precursor and at least one first radical precursor ina first reactant reservoir to form a first reactant stream; combining atleast one second metallic precursor and at least one second radicalprecursor in a second reactant reservoir to form a second reactantstream; wherein the first and second metallic precursors are the same ordifferent; and wherein the first and second radical precursors are thesame or different; flowing the first reactant stream through a firstclear channel section of the reactor which is transparent to activatingradiation used to generate a radical reducing agent from the radicalprecursor to expose the first reactant stream to a radiation source toinitiate a reaction and form a first product stream comprising metallicnanoparticles; combining the produced metallic nanoparticles with thesecond reactant stream downstream of the first clear channel section;flowing the produced metallic nanoparticles and the second reactantstream through a second clear channel section of the reactor that isdownstream of the first clear channel section; exposing the producedmetallic nanoparticles and the second reactant stream to the radiationsource to initiate a reaction and form a second product streamcomprising metallic or bimetallic nanoparticles having a core-shellconfiguration, an alloy configuration, or a combination thereof; andoptionally, collecting the second product stream in a second productreservoir.
 12. The method of claim 10, wherein combining comprisespremixing the metallic precursors and radical precursors in a singlereservoir; and flowing the mixture combined in the single reservoirthrough at least one clear channel section; exposing the mixture in theclear channel section to the radiation source to initiate a reaction andform a product stream comprising metallic or bimetallic nanoparticleshaving a core-shell configuration, an alloy configuration, or acombination thereof; and optionally, collecting the product stream in aproduct reservoir.
 13. The method of claim 10, wherein the radiationsource is an ultra-violet radiation source, a visible radiation source,or a combination thereof.
 14. The method of claim 10, wherein the clearchannel section has a cross-section of from about 1 to about 4millimeters.
 15. The method of claim 10, wherein the metallic precursorcomprises one or more metallic salts.
 16. The method of claim 10,wherein the metallic nanoparticles are gold, silver, copper, platinum,palladium, nickel, lead, or combinations thereof.
 17. The method ofclaim 10, wherein the radical is a ketyl radical or an α-amino radical.18. The method of claim 10, wherein the metallic nanoparticles are about5 nanometers to about 400 nanometers in size.
 19. A continuousflow-through reactor system for producing metallic nanoparticlescomprising: at least one reactant reservoir for combining at least onemetallic precursor and at least one radical precursor in to form areactant stream; at least one product reservoir; at least one channelhaving a first end fluidly connected to the reactant reservoir and asecond end fluidly connected to the product reservoir for flowing thereactant stream there through, wherein the at least one channel has atleast one clear channel section which is transparent to activatingradiation used to generate a radical reducing agent from the radicalprecursor; at least one device for causing the reactant stream to flowfrom the reactant reservoir through the clear channel section to theproduct reservoir; at least one radiation source capable of exposing thereactant stream passing through the clear section channel.
 20. Thecontinuous flow-through reactor system of claim 19 comprising: at leastone first reactant reservoir for combining at least one first metallicprecursor and at least one first radical precursor in to form a firstreactant stream; at least one second reactant reservoir for combining atleast one second metallic precursor and at least one second radicalprecursor in to form a second reactant stream; wherein the first andsecond metallic precursors are the same or different; and wherein thefirst and second radical precursors are the same or different; at leastone first channel having at least one first clear channel section, afirst end fluidly connected to the first reactant reservoir, and asecond end fluidly connected to the product reservoir, for flowing thefirst reactant stream through the first clear channel section to exposethe first reactant stream to a radiation source to initiate a reactionand form a first product stream comprising metallic nanoparticles; atleast one second channel having at least one second clear section, afirst end fluidly connected to the second reactant reservoir, and asecond end fluidly connected to the first channel downstream of thefirst clear channel section, for flowing the second reactant stream andthe first product stream through the second clear channel section toproduct a second product stream comprising metallic or bimetallicnanoparticles having a core-shell configuration, an alloy configuration,or a combination thereof.